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Research Papers

# Bypass Flow Resistance in Prismatic Gas-Cooled Nuclear Reactors

[+] Author and Article Information
Donald M. McEligot

Life Fellow ASME
Center for Advanced Energy Studies, Idaho National Laboratory,
P.O. Box 1625,
Idaho Falls, ID 83415-3560;
Nuclear Engineering Division,
University of Idaho,
Idaho Falls, ID. 83401
e-mail: Don. McEligot@ul.ie

Richard W. Johnson

Mem. ASME
Idaho National Laboratory (Retired),
416 Springwood Lane, Idaho Falls, ID 83404
e-mail: rwjohnson@cableone.net

Manuscript received April 27, 2016; final manuscript received October 20, 2016; published online December 20, 2016. Assoc. Editor: Mark Anderson.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

ASME J of Nuclear Rad Sci 3(1), 011003 (Dec 20, 2016) (9 pages) Paper No: NERS-16-1046; doi: 10.1115/1.4035047 History: Received April 27, 2016; Accepted October 20, 2016

## Abstract

Available computational fluid dynamics (CFD) predictions of pressure distributions in the vertical bypass flow between blocks in a prismatic gas-cooled reactor (GCR) have been analyzed to deduce apparent friction factors and loss coefficients for nuclear engineering systems and network codes. Calculations were performed for vertical gap spacings “$s$” of 2, 6, and 10 mm — representing 1, 3, and 5 mm in a GCR design, horizontal gaps between the blocks of 2 mm and two flow rates, giving a range of vertical gap Reynolds numbers $ReDh$ of about 40–5300. The present focus is on the examination of the flow in the vertical gaps. Horizontal gaps are treated in CFD calculations but their flows are not examined. Laminar predictions of the fully developed friction factor $ffd$ were about 3–10% lower than the classical infinitely wide channel. In the entry region, the local apparent friction factor was slightly higher than the classic idealized case, but the hydraulic entry length $Lhy$ was approximately the same. The per cent reduction in flow resistance was greater than the per cent increase in flow area at the vertical corners of the blocks. The standard $k–ϵ$ turbulence model was employed for flows expected to be turbulent. Its predictions of $ffd$ and flow resistance were significantly higher than direct numerical simulations (DNS) for the classic case; the value of $Lhy$ was about 30 gap spacings. Initial quantitative information for entry coefficients and loss coefficients for the expansion–contraction junctions between blocks is also presented. The present study demonstrates how CFD predictions can be employed to provide integral quantities needed in systems and network codes.

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## Figures

Fig. 1

Idealized representation of the flow cross section formed at the corners of three adjacent hexagonal graphite core blocks [9]

Fig. 2

Idealized representation of the streamwise passage in the vertical gap between graphite core blocks in the “NGNP Point Design” [8,9]

Fig. 3

Predictions of developing laminar flow in the two sections of the 6-mm vertical gap modeled. First section = solid curve; second section = short dashes; and predictions of Schade and McEligot [22] = long dashes

Fig. 4

Predictions for fully developed turbulent flow in ducts. Present k–ϵ results Johnson [17] (RWJ) = solid circles; DNS [25,26] (Kawamura) = solid curve; and empirical correlations by Blasius [27] = centerline; Beavers, Sparrow, and Lloyd [32] (BSL) = dashes; and Zanoun, Nagib and Durst [31] (ZND) = short dashes

Fig. 5

Predictions of developing turbulent flow in the two sections of the vertical gaps modeled: (a) 6-mm spacing and (b) 10-mm case

Fig. 6

Explanation of nomenclature for defining loss coefficients in the junction region

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